The present invention relates to a fuel injector, in particular for an internal combustion engine, with a control rod controlled by the fuel pressure in a control chamber.
Known fuel injectors normally comprise a nozzle having an injection chamber supplied with pressurized fuel for injection; the nozzle has injection orifices which are normally closed by a pin connected to the control rod and activated by the fuel pressure in the injection chamber; and the control chamber has a calibrated fuel intake conduit, and a calibrated, normally-closed control chamber discharge conduit controlled by a metering valve in turn controlled by an electromagnet, which is energized for a variable length of time depending on the amount of fuel for injection.
In known injectors, the control rod is normally arrested mechanically by a fixed stop after sufficient travel to open the nozzle orifices and before fuel injection is completed. The rod is normally arrested by the end wall of the cylindrical rod guide, but, to eliminate precision machining of the end wall of the rod guide, the rod of one known injector is provided with an annular shoulder which is arrested against the edge of the cylindrical guide carried by the usual metering valve body.
In both the above cases, mechanical arrest poses various drawbacks. In particular, it causes a certain amount of shock-induced wear; and, to obtain a predetermined travel, both the fixed stop member and the arrested rod member involve precision machining, complex assembly work, and various provisions to ensure fluidtight sealing between the rod and guide.
It is an object of the present invention to provide a fuel injector of the above type, which is cheap to produce, highly reliable, and provides for eliminating the aforementioned drawbacks typically associated with known injectors.
According to the present invention, there is provided a fuel injector for an internal combustion engine, the injector having a control rod controlled by the fuel pressure in a control chamber, and comprising a nozzle having an injection chamber supplied with pressurized fuel for injection; said nozzle having at least one injection orifice normally closed by a pin; said pin being connected to said rod and being activated by the fuel pressure in said injection chamber; said control chamber having a pressurized-fuel intake conduit and a fuel discharge conduit; said discharge conduit being normally closed and being opened for a variable length of time; and the injector being characterized in that said pin and said rod, and/or said intake conduit and said discharge conduit, are so sized as to keep said pin and said rod hydraulically balanced in a maximum-lift position to open said orifice.